1. Field of the Invention
The present invention relates to a molded electronic circuit device wherein an electronic circuit having a heat-radiating electronic element is molded in a case with a resin.
2. Description of the Prior Art
Electronic circuits incorporating small electronic elements are generally encapsulated such that a synthetic resin material is filled between electronic parts and elements so as to improve reliability and resistance to vibration, humidity and dust. The electronic circuits and elements are molded in a case as a single unit. A synthetic resin material for molding comprises a thermosetting resin such as epoxy resin, polyimide resin, polyester resin or polyamide-imide resin. However, thermosetting resins are easily influenced by temperature changes. The performance or function of the electronic elements molded by a thermosetting resin and hence their reliability is degraded by humidity.
Silica (silicon oxide), which has a high resistance to humidity, can be used as the resin material. However, silica has a low thermal conductivity and therefore cannot be used as a material for molding an electronic circuit having heat-radiating electronic elements. Some materials which have good thermal conductivity are aluminum oxide, magnesium oxide, beryllium oxide or the like. However, such a material has hygroscopicity. The oxide is not completely hardened, or insulation between the electronic elements and circuits is degraded. In addition to these disadvantages, moisture is absorbed in the resin, and this causes degradation in the performance or function of electronic elements. The oxide cannot be used as a molding material without modification.